The invention relates generally to the field of teletherapy and in particular to a system and method for identifying morphological changes in a target tissue.
Teletherapy is defined as a treatment methodology in which an irradiation source is at a distance from the body to be treated. X-rays and electron beams have long been used in teletherapy to treat various cancers. Unfortunately, X-rays and electron beams exhibit a linear energy transfer approaching an exponential attenuation function, and are therefore of minimal use for deeply embedded growths. Recently, the use of heavy particles, particularly hadrons, in teletherapy has found increasing acceptance, due to the ability of heavy particles to penetrate to a specific depth without appreciably harming intervening tissue. In particular, the linear energy transfer of hadrons exhibits an inversed depth profile with a marked Bragg peak defined as the point at which the hadrons deposit most of their energy, and occurs at the end of the hadron's path. As a result of this effect, increased energy can be directed at an embedded growth as compared to X-rays and electron beams, which particularly harm intervening tissues. While the term hadrons include a wide range of particles, practically, protons and various ions are most widely used in teletherapy.
Treatment planning and follow up is a critical factor in teletherapy so as to accurately determine the appropriate dose distribution for a target tissue, while causing minimal damage to adjacent tissues. In certain cases, such as where the target tissue is in the chest cavity, a series of scans of the target tissue and surrounding area are taken, to develop a four dimensional image of the target tissue area. In particular the four dimensional image represents a series of three dimensional images over the complete breathing cycle, with each scan thus representing a particular phase of the breathing cycle. The scans may comprise x-ray scans, computerized tomography (CT) scans, positron emission tomography (PET) scans, or ultra-sound (US) scans, without limitation. A treatment plan is then developed in relation to a single one of the plurality of phase scans, i.e. while all of the scans may be viewed and utilized, the treatment plan is developed and described in relation to a single one of the plurality of scans. This particular one of the scans is denoted hereinafter the treatment plan phase scan.
Irradiation of the target tissue, in the case of organs whose position vary over the breathing cycle, may be performed by gating the irradiation to occur only during the portion of the breathing phase consonant with the phase of the treatment plan phase scan. Alternatively, irradiation may be performed continuously over the entire breathing cycle, with the treatment plan taking into account movement of the target tissue over the breathing cycle.
Pre-treatment imaging is an important part of teletherapy and is particularly important in obtaining precise location information of the patient as well as updated information regarding the diseased tissue to be irradiated. Location information of the patient is required for accurate positioning of the patient in relation to the irradiation beam, and updated morphological information is used to update the dose distribution determined at the treatment planning stage.
Prior art methods of pre-treatment imaging exist based on x-ray technology, wherein an x-ray image, or a pair of orthogonal x-ray images, is taken of an immobilized patient in position for irradiation. The x-ray image, or a pair of orthogonal images, is compared with synthetic x-ray images derived from a reference computerized tomography (CT) scan for which the initial treatment plan is described, and any location adjustments are performed. The synthetic x-ray image is often called a digital reconstructed radiograph (DRR). The pre-treatment x-ray image, or pre-treatment pair of orthogonal x-ray images is compared with the treatment plan phase scan, and thus precise positioning is performed.
Unfortunately, no morphological updates of the treatment planning are taught in the prior art.